Determination of Na+, K+, Mg2+, and Ca2+in seawater is currently performed by using either laborious wet chemical methods or physical ones requiring complicated and expensive instruments. The present study assessed the feasibility of using capillary electrophoresis (CE) as an alternative method for analysis of these metal ions in seawater samples and the robustness of CE in determination of the metal ions in samples of complex matrices. Imidazole was added in various electrophoretic media to provide UV absorbing background for indirect detection and 18-crown-6 was utilized to manipulate selectivity through complexation. Na+, Mg2+, and Ca2+in seawater samples could be determined in an electrophoretic medium of 40 mM 18-crown-6 and 10 mM imidazole at pH 4.5 with an internal standard of Li+, but quantitative determination of K+had to be carried out in another separate run by using an electrophoretic medium of relatively low concentration of 18-crown-6 to improve the precision of the quantitative results. It was demonstrated that CE could be a fast, simple and low cost means for the determination of Na+, K+, Mg2+and Ca2+in seawater with fairly good robustness.